The following is a chronological catalog of archival documentation pertaining to the early history of Fitch's knowability paradox. The items were identified for the first time by myself or those aiding my research. My discussion of their content appears in "Knowability Noir: 1945-1963", which is forthcoming in New Essays on the Knowability Paradox.
An edition of this and the second referee report (listed below) is being prepared by Julien Murzi and myself for publication in New Essays on the Knowability Paradox. Here's an appendix of the logical resources therein.
(FFP) Frederic B. Fitch Papers: Manuscripts and Archives. Yale University Library.
(ACP) Alonzo Church Papers: Department of Rare Books and Special Collections. Princeton University Library.
(ENP) Ernest Nagel Papers: Rare Book and Manuscript Library. Columbia University.
(from Referee Report 1)